1. Field of the Invention
The present invention relates to an oxidation inhibitor, particularly useful for preventing scale formation on metal product at high temperatures.
2. Description of the Prior Art
Conventionally, the steel products have been produced according to the following process:
Steel making.fwdarw.ingot making.fwdarw.soaking.fwdarw.breaking-down rolling (slab manufacturing).fwdarw.surface conditioning.fwdarw.heating.fwdarw.rolling.fwdarw.steel products. PA1 Surface conditioning.fwdarw.heating.fwdarw.rolling.fwdarw.steel products.
In case where continuous casting is adopted, the slabs are subjected to the following steps:
The ingots and the slabs are heated at high temperatures in the soaking furnace and the heating furnace for a long time in the above conventional production processes, so that a large amount of scale is formed during the heating, resulting in considerable lowering of the production yield and causing a great problem from the point of saving the iron source.
In order to overcome the above difficulties and problems, various types of oxidation inhibiting methods have hitherto been proposed and published. Some of these known methods prevent the oxidation by forming a layer of ceramics, glass or the like on the steel surface by baking; others of the methods prevent the oxidation by precipitation of oxide crystals on the metal surface, still others of the methods spray a metal or an inorganic salt having a relatively low melting point on the metal surface and heat the metal or salt, and still further others of them coat the metal surface with a heat-resistant organic substance, or combine these known technics.
By any of these conventional methods, excellent oxidation prevention can be assured at low-temperature zone up to about 800.degree. C., but this excellent oxidation prevention sharply lowers when the temperature exceeds about 1000.degree. C., and in some cases the oxidation inhibitor reacts with Fe of the metal surface, causing dissolution of Fe in the form of Fe.sup.++ which is hinderous to the oxidation prevention.
Further, in case of flame plating, plasma jet welding, physical and chemical vapour deposition for forming the oxidation inhibiting layer, a treating apparatus of large scale is required and the treating cost is high. Some reports have been published on other methods in which refractories are applied on the steel surface or special chemical treatments are effected.
In general, the oxidation inhibitor is required to have a good removability during a hot rolling as well as an excellent oxidation inhibiting property.
Thus, when the oxidation inhibitor applied on a steel slab, which is then heated and rolled, is entrapped into the slab surface during the hot rolling, it causes surface defects and lowers the commercial value of the product remarkably. Thus it is necessary to remove the oxidation inhibitor as much as possible, preferably completely, by a scale breaker during the hot rolling. No satisfactory oxidation inhibitor has been developed which has both good oxidation preventing property and good removability.
The present inventors have made extensive studies and experiments for development of an oxidation inhibitor having the both excellent oxidation preventing property and good removability as disclosed in Japanese Laid-Open Patent Specification No. Sho 49-30237.
The oxidation inhibitor disclosed in this Japanese Laid-Open Patent Specification can prevent formation of scale almost completely even in case of a high temperature heating above 1000.degree. C., particularly 1200.degree. C. for a long time, and can reduce the scale formation to 1/500-1/1000 of that formed when no treatment with the oxidation inhibitor is done.
However, it has been found that the oxidation inhibitor disclosed in the above Japanese Laid-Open Patent Specification does not always show satisfactory removability when heated above 1300.degree. C. or applied to a special steel grade in spite of its excellent removability in case of an ordinary hot rolling.
Therefore, the present inventors have made various studies and experiments to improve the removability of the oxidation inhibitor during the hot rolling and developed various methods for improving the removability as disclosed in Japanese Laid-Open Patent Specification Nos. Sho 49-43809, Sho 49-63611, Sho 49-73314, Sho 50-5207 and Sho 50-5208.
By combining the oxidation inhibitor disclosed in Japanese Laid-Open Patent Specification No. Sho 49-30237 and the methods just mentioned above, it is possible to apply the oxidation inhibitor to all kinds and types of steel.
For example, this combination will provide the greatest advantage in case of a special steel, such as 9% Ni steels, stainless steels and copper-containing steels, which is very susceptible to intergranular oxidation and selective oxidation due to very slight oxidation, and hence very susceptible to cracking during the hot rolling and surface defects caused by the entrap of hardly-removable scale into the rolled surface.
Meanwhile, in case of ordinary steels which are produced in a large amount, the production cost is low so that oxidation inhibitors used for these ordinary steels are not required to have excellent oxidation prevention as required in case of the special steels, but it is required that they can be produced at a lower cost, with simpler treatments and drying, and have good removability during the hot rolling.
The present inventors have further conducted studies and experiments and have developed an oxidation inhibitor which is advantageous technically and economically for both ordinary steels and special steels.